Speeds and Feeds, getting an excellent surface finish in BDMS

I'm turning a conrod from a BDMS square bar. The round part will be vary from 6 - 8mm over its length. It's fat in the middle.
I'm using the topslide for the taper, bad mistake as I've denied myself access to fine feed the tool.
Anyway with very light cuts, super sharp HSS tool and lots of cutting oil, the tool is still picking up occasionally and spoiling an otherwise nice finish. The tool is "standard" pattern with a round nose 1/8 inch radius.
I'm running the spindle at 1000rpm. Faster doesn't seem to help. Is this as good as its going to get?
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Steve wrote:

I don't know where the "big nose is good"-rule*) comes from. But its almost always wrong. A big radius works good with a big cutting depth, but you don't have that. Try it with a 0.2 .. 0.4 mm radius.
*) Big bubbles, no troubles? <G>
Nick
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Nick Mueller Wrote:

Hi Steve, Nick is right, a large radius requires more power to work, a larger surface area means more friction. This is OK on big lumps of metal but your con-rod is not large, and will bend or flutter with your tool. A small tip radius and finer feed than radius, should help, all things being equal. Had you thought to turn your fishtail with a hand tool? Ned Ludd
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Thanks guys, I'll go and apply some HSS to the grinder...
Hadn't thought of turning this by hand, the method here is turn two tapers from the centre leaving the centre over finished dimension by about 1mm, then turn the centre section parallel and "finish with files"...
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And oil and abrasive papers...
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Steve Wrote:

We expect to hear the results, so report back. Ned Ludd
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Beautiful finish using oil an abrasives, then milled 1.5mm of the wrong side aargh!!!
Will post a picture when I get chance.
Steve

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-
Treat as a practice piece. You now know you can get it right.
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Steve wrote:

But I hope the finish was OK!
Ni-you're not alone-ck
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The finish was fantastic...
One trick I have adopted is if I scrap a part I do follow through to the end, "practice piece" as Gunsmith said so I know how to make the repeat. The other reason is that one complex part I threw in the scrap in disgust, whilst having a brew I suddenly realised how to recover the mistake, which worked fine, except it was bruised from being thrown in the bin!!!
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Steve wrote:

Me too! Especially if doing several of the same. In the end, I do have one (or two*) ) scrap parts. In the later steps, that scrap often helps saving time for setup.
*) But I only plan for one scrap. :-))
Nick
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